Assessing the Sulfur Status of Field‐Grown Wheat by Plant Analysis1

Abstract

AbstractDiagnostic methods developed under laboratory or greenhouse conditions require field confirmation. This paper reports the relative field performance of four indexes for the diagnosis of S deficiency in wheat (Triticum aestivum L.) which were previously assessed in the greenhouse. Sulfate S (as percent total S), sulfate S concentration (as ppm dry matter), total S concentration (as ppm dry matter), and total N: total S ratio in the aboveground parts of a soft white wheat cultivar, ‘Olympic’, were compared as diagnostic indexes in a factorial experiment with five rates of gypsum (0 to 50 kg S/ha) and three rates of ammonium nitrate (0 to 100 kg N/ha). A strong relationship was found between final grain yield and each index at the following stages of growth; fourth leaf (61 days from sowing), fully‐tillered (92 days), and jointing (134 days). However, as the critical value for sulfate S (as percent total S) was least affected by the age of the plant or N supply, it is considered to be the most convenient index. The overall relationship between yield and sulfate S (as percent total S) was strong (r = 0.88) and the critical value at 90% of maximum yield was 13%. This compares with r values of 0.87, 0.96, and 0.91 and critical values of 14, 12, and 11% for the plant tissue at the individual growth stages examined. Where the adequacy of the S supply to a wheat crop is in question, the proportion of total S as sulfate S in the plants is indicated as a useful guide to the need for S fertilizer in securing optimal grain yield.